Extending estimating Hydrogen content in Atom Probe Tomography where H2 molecule formation occurs


The voxel based extrapolation of H(a) and H(b) in extrap-freq-High rate.  A region of increased H content is seen on the top of the tip, possibly corresponding to a surface oxide.

A team from the Research Group in Atom Probe Tomography at Oxford, and the University of Friedrich-Alexander in Germany, investigated a new method for estimating specimen hydrogen content in atom probe tomography (APT) in experiments where molecular hydrogen ions originating from the measurement environment can overlap with deuterium in the mass-to-charge-state spectrum (which prevents the direct application of isotopic marking for unambiguous analysis).

The team began by applying an existing method for hydrogen content estimation (using ratios obtained from paired deuterated/nondeuterated experiments).  The measurements demonstrated sufficient residual uncertainty to motivate exploring an alternative method to accurately estimate hydrogen content).

By varying the time between evaporation events, a highly correlated relationship between field evaporation rate and hydrogen content was noted; this led to the team developing a new method for measuring hydrogen content within the specimen.  They combined this extrapolation technique with continuous cycling of the evaporation rate or pulse frequency during an APT experiment.  This could enable spatially resolved imaging of hydrogen concentrations despite the presence of a contaminant bckground hydrogen signal, without the need for deuteration.

The full paper ('Extending estimating Hydrogen content in Atom Probe Tomography experiments where H2 Molecule formation occurs' is published by Microscopy and Microanalysis.